Bacterial skin infections, especially by Staphylococcus aureus, can both initiate and propagate many inflammatory skin diseases, particularly atopic dermatitis (AD). The mechanisms by which this occurs are unclear, but many lines of evidence implicate the involvement of biologically active staphylococcal bacterial products such as superantigen toxins, alpha toxin, and the cell-wall lipoprotein lipoteichoic acid (LTA). The ability of these staphylococcal products to stimulate cytokine production in keratinocytes could provide one mechanism by which staphylococcal skin infections worsen AD. Both preliminary and published data from our group indicate that the lipid mediator platelet-activating factor (PAF) can modulate the effects of these bacterial products on keratinocyte cytokine production. Three specific aims are planned to help define the mechanism(s) by which bacterial products worsen skin disease which will allow novel treatment strategies for patients with infected atopic dermatitis. The first objective will define the levels of these staphylococcal products on clinically infected AD lesions, and generate biologically active wash fluid from infected AD lesions for further studies for both this Project as well as for Project 2. The second aim will use two novel model systems with PAF-R and toll-receptor-positive and -negative epidermal cells to define the role of the PAF-R versus toll-like receptors in bacterial productmediated cytokine production. The third objective will examine the ability of bacterial products to induce cutaneous inflammation both in wild-type and a novel mouse model of atopic disease (StatGVT mice). PAF-R-/- and MyD88-/- mice will be used to define the role of the PAF and toll-like receptor system in these processes.